The first time I ran it there was a long delay between seeing Checking prospero.unm.edu... and seeing evidence of file transfer. The whole prospero thing took 7:19 and it downloaded everything. The second time I ran it, the prospero thing took 6:13 and it downloaded nothing (expected). The third time was like the second (6:13 again). In all cases the BTM choked when it got to the 7Z stuff.
I imagine prospero's upstream bandwidth is limited, or the FTP server limits per-connection transfer speed.
It doesn't look like there's anything wrong.
You might make a suggestion (suggestion forum) that TCC show messages like this.
ftp://prospero.unm.edu/tcmd/v8/version.txt ... up to date
It would be nice if COPY /U had more status messages. Especially if there are a lot of files/folders being checked. Please see the folloowng thread for more.... https://jpsoft.com/forums/threads/copy-u-with-a-ftp-site.11154/#post-63033
Heck! Make a complete list, with file names, and copy them one at a time. I doubt it would take significantly longer if you used IFTP. I haven't tested, but in a perfect world, _? will be zero if the file was copied and non-zero otherwise. If that's so, you could have a status report for every file.